Specific solvent effects on the charge separation efficiency in photoinduced electron transfer processes

GRACIELA P. ZANINI; HERNÁN A. MONTEJANO; CARLOS M. PREVITALI

JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY

Elsevier

Año: 2000 vol. 132 p. 161 - 166

1010-6030

The photoinduced electron transfer (PET) quenching of singlet excited pyrene and 1,2,5,6-dibenzanthracene (DBA) by 3-cyanopyridine and o-dicyanobenzene, respectively, was investigated in several protic and aprotic solvents. The triplet quenching of DBA by p-nitrobenzaldehyde was also studied in the same solvents. In all cases free radical ions yield were measured by laser flash photolysis. In the case of the triplet reaction, forward electron transfer quenching rate constants were also measured. Charge separation efficiencies, cs were determined from the free radical ions yields. The solvent effect on cs in singlet state PET may be explained in aprotic solvents by a model based on the macroscopic properties of the solvent. For alcohols the efficiencies are lower than the corresponding quantities for aprotic solvents of similar viscosities and dielectric constant. For triplet mediated PET reactions, the forward rate constants are scarcely sensitive to the solvent, while strong specific solvent effects are important in determining the back-electron-transfer to ground state.